Geographic reuse of carrier frequencies has proliferated as a viable solution to the problem of limited radio spectrum in cellular radiotelephone systems. Traditionally, a served area is subdivided into clusters of cellular coverage areas which have allocated to them groups of carriers. These clusters are repeated such that carriers reused from cluster to cluster are sufficiently geographically separated from one another to permit simultaneous reuse of carriers without undo interference.
Frequency hopping might be employed to provide sensitivity improvement against slow fading and to improve carrier-to-interference (C/I) margin in cellular radiotelephone systems. Transmissions within a given coverage area would be hopped from one carrier within the group allocated to that coverage area to another within the group, hopping from one to another. However, there must be a sufficient number of carriers in each coverage area over which to hop or the advantages of frequency hopping are diminished. In other words, both less dense cellular reuse and greater frequency hopping improve the performance in a given coverage area, but both usually draw from the very same (and scarce) spectrum. So, whatever is gained by one technique is gained at the expense of the other.
In currently-proposed Time-Division, Multiple Access (TDMA) cellular systems, particularly when utilized as an adjunct to preexisting analog cellular systems or where more than one operator coexist, fewer carriers are available to be employed, or are required for that matter, because up to eight conversations take place in eight repeating timeslots on a single carrier. Accordingly, up to seven-eighths fewer carriers are required to carry the same channel capacity. This reduction in carriers available to each coverage area reduces the opportunity for employing frequency hopping as an effective system enhancement.
This invention takes as its object to overcome these shortcomings and to realize certain advantages presented below.